Abstract
Spatial modulation (SM) utilizes the transmit antenna index and a quadrature amplitude modulation (QAM) symbol chosen from a constellation diagram to improve spectral efficiency (SE) comparing to conventional modulation scheme. However, in the conventional SM system, the modulation mode applied to the active antenna is fixed, which degrades the bits error rates (BER) and spectral efficiency (SE) performance. Moreover, a large number of researches on SM systems focus on the utilization of the uniform linear array (ULA) for transmission, which only considers the transmission on the horizontal domain while ignoring that on the vertical domain. Therefore, in this paper, we propose an adaptive spatial modulation (ASM) scheme with uniform planar array (UPA) over millimeter wave (mmWave) channels, which combines SM with adaptive modulation (AM) to enhance the performance of SE. To further improve the bits error rates (BER) performance, we develop an UPA-based ASM scheme with transmit antenna selection (TAS). We then analyse the BER and SE performance of both the two ASM scheme and obtain the closed-form expression for SE of the UPA-based ASM scheme with TAS algorithm. The simulations demonstrate that the proposed ASM schemes can achieve a considerable SE and a relatively low BER.
Highlights
Nowadays, the spectrum at microwave frequency bands becomes scarcely, which limits data rates, whereas the spectrum in the millimeter wave realm ranging from 30GHz to 300GHz is abundant
In order to reduce the complexity of detector and improve bits error rates (BER) performance, we further develop an uniform planar array (UPA)-based Adaptive spatial modulation (ASM) scheme with transmit antenna selection (TAS-UPA-based ASM scheme), in which a column of antennas is selected according to source bits while the activated antenna is chosen from that column of antennas via transmit antenna selection (TAS) algorithm
The gap of spectral efficiency (SE) between the UPA-based ASM scheme and the uniform linear array (ULA)-based ASM scheme is obvious in the low SNR region because the number of transmit antennas dominates the SE performance
Summary
The spectrum at microwave frequency bands becomes scarcely, which limits data rates, whereas the spectrum in the millimeter wave (mmWave) realm ranging from 30GHz to 300GHz is abundant. The ASM scheme is designed to improve BER performance with an exhaustive search of the optimal transmission mode according to the CSI, which is of high complexity [22]. ASM schemes are dedicated to reduce the complexity with the exhaustive search strategy by shrinking the search space [23, 24] Both the modulation order assigned to each antenna and the number of activated antennas are adaptive to channel conditions [25]. The proposed UPA-based ASM scheme adjusts the modulation mode according to the CSI with the aim of SE improvement while maintaining the BER under the acceptable BER target.
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